Characterization on p H sensing performance and structural properties of gadolinium oxide post-treated by nitrogen rapid thermal annealing

A detail investigation on the pH sensing performance of Gd2O3 layer was proposed in this work. Electrolyte–insulator–semiconductor (EIS) structure with Gd2O3 layer deposited directly on silicon by reactive radio frequency sputtering with Gd target was chosen as the testing platform. The postdeposition rapid thermal annealing (RTA), performed at various temperatures for 1 min in N2 ambience, was first used to improve the pH sensing performance of Gd2O3. With RTA treatment at 800 °C, pH sensitivity of Gd2O3 EIS structure can be increased from 35.5 mV/pH to 55 mV/pH. This behavior can be explained by the increase of surface sites, which is supported by atomic force microscopy analysis. With RTA treatment at 700 °C and 800 °C, the drift coefficient for Gd2O3 layer was reduced to 0.03 and 1.2 mV/h, which is resulted from the densification of Gd2O3 layer supported by x-ray photoemission spectrometry. Therefore, Gd2O3 layer with RTA in N2 ambience at 700 °C or 800 °C could be a potential candidate for pH-sensitive membrane.